The invention relates to surface treatment assemblies. More specifically, the invention relates to an abrasive assembly which presents a workpiece to be surface treated with at least two separate abrading surfaces, with each abrading surface having different abrasive characteristics, to a method for making such an abrasive assembly, and to its use.
Surface finishing of a workpiece can include sanding, buffing, polishing or other finishing processes. A wide variety of materials for such finishing have been used. For example, sandpaper of various grades and nonwoven finishing pads with abrasive coatings or additives are well known. One manufacturer of sandpaper products is Minnesota Mining and Manufacturing Company, St. Paul, Minn. Sandpaper sheets in various configurations and abrasive grades, double-sided abrasive sheets ("duplex" sheets), as well as abrasive sheet material where one side has abrasive and the other side has pressure sensitive adhesive, are all well known. Nonwoven pads having a variety of surface treatment characteristics (and in varying abrasive grades) are also available from Minnesota Mining and Manufacturing Company, St. Paul, Minn., commercially referred to as SCOTCH-BRITE.TM. pads.
Although these surface finishing materials can be used to refine nearly any surface, they have found particular application to floor refinishing techniques. It is common in floor sanding to use a nonwoven abrasive pad on a rotary sander machine as a cushion between the sander and a sandpaper sheet facing the floor. An abrasive disk of sandpaper of the same size or larger than the circular face of the nonwoven pad is either mechanically fastened from its center to the sander, or mounted relative to the nonwoven pad via use of a double-sided abrasive disk or affixed by a pressure sensitive adhesive on the back of the disk to adhere the disk to the nonwoven pad. Mechanical fastening of a sanding disk from its center requires the use of a full abrasive disk, which reduces unit pressure for sanding, limits the ability of the sandpaper to conform to the floor surface, and wastes the abrasive in the center of the disk. Double-sided abrasive disks rely on a loose mechanical bite between the back abrasive side and the nonwoven disk to maintain those components attached for coupled rotation. The use of a pressure sensitive adhesive to mount the sandpaper to the nonwoven pad allows the placement of a disk over the face of a pad. However, the pressure sensitive adhesive may not hold well to the non-uniform fibrous face of the nonwoven pad, especially if the pad has any dust or debris built up on it, which is very common in finishing operations (e.g., sanding of drywall, cabinets, furniture, automobiles and similar operations that generate fine sanding dust) and in the hostile workplace environment in which such operations often take place. Increasing the density of the nonwoven pad provides additional fiber surfaces for pressure sensitive adhesive bonding, but may not be desired for other functional reasons.
For some floor finishing situations, a strip of sandpaper is mounted across the face of an abrasive nonwoven disk to present two different abrasive surfaces to the floor for surface treatment. The sandpaper strip is secured in place relative to the nonwoven pad either by folding the sandpaper over so the abrasive is on both sides of the sandpaper sheet, or by just folding over the edges of the sandpaper sheet, or by using a pressure sensitive adhesive disposed on the back of the sandpaper sheet. None of these attachment alternatives has resulted in a connection between the sandpaper and the nonwoven web which is sufficiently simple, reliable and repeatable in the dusty, non-uniform and hostile (and rapidly rotating) floor sanding environment.
As a floor surface is treated, it may be necessary to substitute a fresh sheet of sandpaper, or it may be desired to change to a sandpaper sheet having a different abrasive grade. After initial use, this may not be possible using a pressure sensitive adhesive backed sandpaper on a nonwoven pad because the dust on the pad prevents a second sandpaper sheet from adhering to the pad. Thus, not only is a different sheet of sandpaper required for further finishing, but a clean nonwoven pad is also required, in order to adhere the sandpaper to the nonwoven pad. The existing (dirty) nonwoven pad must be cleaned or a new nonwoven pad used. This is especially troublesome for applications where it is desired to arrange a sheet of sandpaper on the face of a nonwoven pad which is smaller than the nonwoven pad, so that the abrading surface presented to the floor includes not only the sandpaper but also the abrasive on the nonwoven pad itself. Prior to the present invention, there has been no truly effective means for affirmatively securing a sandpaper sheet across a portion of a nonwoven abrasive pad for use in creating an abrasive assembly which presents multiple abrasive surfaces for workpiece surface treatment.